In many wireless communication systems, a user equipment must first perform a random access procedure with a base station to fight for a chance of establishing connection with the base station, and mutual data transmission between the user equipment and the base station can be achieved only after the connection is established therebetween. For example, under the architecture of Narrow Band Internet of Things (NB-IoT), the user equipment may establish connection with the base station according to the random access procedure specified by the Long Term Evolution (LTE), and the random access procedure comprises the transmission of the following five messages, which are respectively as follows: the user equipment transmits a random access request message (which is called a first message for short) to the base station; the base station transmits a random access response message (which is called a second message for short) to the user equipment; the user equipment transmits an RRC connection request message (which is called a third message for short) to the base station; the base station transmits an RRC connection setup message (which is called a fourth message for short) to the user equipment so that the user equipment enters an RRC connected mode; and the user equipment transmits an RRC connection completeness message (which is called a fifth message for short) to the base station.
According to the random access procedure specified by the LTE, the connection between the user equipment and the base station can be established only after the aforesaid five messages all take effect, and if any of the aforesaid five messages cannot take effect, then the corresponding message must be re-transmitted. In other words, mutual data transmission between the user equipment and the base station can be achieved only after the transmission of at least the aforesaid five messages, and if any of the aforesaid five messages cannot take effect during the random access procedure, then the user equipment must wait for more time to achieve mutual data transmission with the base station. Obviously, such a transmission manner will reduce the transmission efficiency of the data and the utilization ratio of the resource. Accordingly, an urgent need exists in the art to improve the aforesaid random access procedure so as to improve the transmission efficiency of the data and the utilization ratio of the resource.